Sorry if I missed it but Hogwarts Express is taking people from Universal to Islands right? Going tomorrow/Wednesday and staying on property with Express so will do Universal first before descending on whatever madness is happening with Hagrid. So either
A.) they won't let people queue up and will instead just ferry them through Hogsmeade to prevent people from clogging the walkway, which is what they do whenever they have the nighttime show on the castle, or
B.) they'll let people line up for hours and the ride will open with a 3-4 hour wait right off the back, though if it's running consistently hopefully that falls.